Analogue-sequencer

> I had the specified 6N139 device originally, and even though I could 
> pass midi data quite happily using mthru on the P3, it was giving me 
> problems with loading large blocks of data.
> 
> On a hunch, I thought I'd replace the opto, with a pin compatible 
> device, HCPL-4701, which has a higher current transfer ratio (600% 
> compared to 400%).
> 
> B*gger me, it worked first time. Just to check, I popped the 6N139 
> back in, and it was still not playing the game, so I took it out, 
> dropped it on the floor and squashed it.

That's really bizarre. I've never had a problem with the 6N139, so I
guess there may have been some damage to the one you were using (static
?).
It'd be interesting if you get a chance to try another 139 and see if it
works OK.
Why the part would work OK for bursts of data like note messages and
short sysex blocks, but stop working during a large continuous block I
can only guess - maybe some stray capacitance at work...

Anyway, glad to hear you got it fixed !

Cheers,
Colin f